1995 Chevy S-10 4X4

This is a easy one. In most cases you will find a bad transfer case vacuum switch that cost about 20 bucks. When applying 4wd the transfer case is shifted manually througha shift fork to engage the front driveshaft (we know that is working) the tranfer case then applies pressure on the front drive vacuum actuator located on the drivers side top of transfer case. This switch is usually frozen causing it not to send vacuum to the front drive actuator, thus causing front wheel not to lock. There are other possibilities but this usually fixes it 90 percent of the time.

You will need a short 7/8 wrench to remove it. I cut a old craftsman wrench in half to make job real easy